Welcome on the new wip for the part4.
This month, I search some ideas for the futur special effects of the movie. For many times you ask me to explain more the construction of my work. Here's an example:
To make a tornado, the most important is the speed change of the rotation. On the ground the column turn faster than the upper. In fact the wind did not change speed but as the diameter increases, the speed of the rotation decreases.
I must therefore create an object that shows this effect. It should be useful to setting the speed change between the ground and the sky. The basic object shows the shape of the tornado. Then, I separate the object in horizontal slice.

Now, I pile the objects so that a portion of each object is superimposed. The superimposed part coincides with the alpha mask texture. This setting is necessary for the effect of the tornado. I select all the objects and do several rotation. now they have the same speed of rotation.

On the scene editor, all cursor objects are aligned. By moving the dimensioning tool I can vary the speed rotation of each slice. The difference in rotation between the slices will be attenuated (in the render) by the alpha mask of the textures. It look like a smooth transition of the speed between the slices. Note the Clip area (red) represent that i need. What is useful is you have a visual idea of the variation of the speed. Here, base0 (ground) have a speed x20 than base 8 (sky). The others objets are a duplication of the base to create debris around the tornado (with the transparency shader eroded). Just I change the diameter and the speed. I use a layer for each complete column.